Process of inhibiting the oxidation of hydrocarbons



` the stabilization of hydrocarbon Patented Oct. 28, 1941 UNITED STATES PATENT 'OFFICE i PROCESS OF INHIBITING TBE OXIDATION OF IIYDROCARBONS Wilbur E. Robbins, Norco, La., and Richard B..

Zundel, Wood River, IIL, assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application September 7,1939, Serial No. 293,708

claims.

This invention relates to a process v-of inhibiting -oxidation of hydrocarbons by the use of alkyl phenols as anti-oxidants and gum inhibitors and more particularly is concerned with lthe use of certain fractions of crude alkyl phenols in hydrocarbon oils as anti-oxidants vand gum inhibitors which have a greater effectiveness in this function than the ordinary bulk alkyl phenols.

Alkyl phenols from various sources such as petroleum and coal tar, and various distillation cuts of these alkyl phenols have been used as antioxidants in gasolines and-the like. However de- -spite the v.fact that these inhibitors are readily available and inexpensive, their use has been greatly limited because of the fact thata comparatively large quantity must be added to secure the inhibiting effect produced by a much small- .er quantity of many other inhibitors such as amino phenols, aromatic diamines, etc. It is an object of this invention. to provide alkyl phenol fractions of high inhibiting value which may be inexpensively and easily prepared from crude alkyl phenols or their distillation fractions of ordinary inhibiting value or from some readily available source of alkyl phenols such as petroleum or coal tar fractions.

It has already been suggested fractionally to distill alkyl phenol fractions and to select those fractions for inhibiting purposes which are most active. However, while there may be some diflierences in the effectiveness between various fractions so obtained, these diierences are normally very small and insignicant.

Now we have found that the relatively weakly acidic alkyl phenols are more effective as inhibitors thanthe more strongly acidic alkyl phenols Vhaving similar boiling points-or approximately the same molecular weights, and that the -eifectiveness as inhibitors of themixtures of the alkyl phenol fractions rises rapidly with decreasingacidity.

The superior inhibiting effect of the more weakly acidic alkyl phenols can be observed under various conditions, and does not seem to be specific to the stabilization of certain types of materials. In general, wherever alkyl phenol mixtures are active anti-oxidants, the more weakly acidic portions of the mixture are more active than the. total mixtures. This applies to oils, such as cracked gasolines, rubber, paints, etc.

The weakly acidic fractions maybe prepared inexpensively and conveniently by fractional exinsoluble solvent for alkyl phenols. method is generally advantageouswhen produc-.

traction of crude alkyl phenol mixtures with caustic alkali such as aqueous solutions of sodium hydroxide, the more strongly acidic fractions being extracted by the caustic alkali forming extracts, and the more weakly acidic ones forming raiflnates. By crude alkyl phenol mixture is Vmeant a mixture consisting predominantly of alkyl phenols boiling above about C. which may contain substantial amounts of impurities such as thiophenols and which has been obtained from coal tar or petroleum distillates by extrac- 'tion with strong aqueous caustic alkali and acidification of the extract. A preferred methodfor producing crude alkyl phenol mixtures is described in U. S. Patent 2,134,390 by /Greensfelder et al. According to this patent alkylphenols are recovered from hydrocarbon distillates containing them, by treating with aqueous solutions of alkali metal hydroxides having concentrations between 30 and 50% and acidifying the resulting aqueous layer to liberatethe alkyl phenols. If desired alkyl phenols may be extracted from distillates by treatment with aqueous caustic solul tion containing solutizers such as salts of lower fatty acids having from 2 to 6 carbon atoms, poly-hydroxy alcohols having a greater number of carbon atoms than polar radicals, etc.

The separation of even a small amount of the most strongly acidic components from the crude alkyl phenol mixtures often may cause a marked increase in inhibiting value of the resulting raffinate. Most crude alkyl phenols, vand especially those derived from petroleum, normally contain appreciable quantities of thiophenols which usu` ually have a decided detrimental effect'on the inhibiting value of the alkyl phenols. Further removal from the crude alkyl phenol mixture of successive quantities of relatively strongly acidic` fractions leaves rafiinates of increasing inhibiting value. Generally in order to obtain raffinate fractions of greatest inhibiting value it is desirable to recover as a raiiinate not more than about half of the total crude alkyl phenols. Such raiiinate fractions may have inhibiting values up to four or even more times those of the crude phenols from which they were extracted.l

The fractional extraction to separatethe crude alkyl phenol mixture into fractions of differing I inhibiting powers may be carriedl out as a counter-current or crosscurrent process and, if de f sired, in the presence of a substantially water- The former ing one fraction of high inhibiting value from sources having rather large amounts of impurities while the latter is often best adapted, where several cuts may be taken from a crude mixture which contains smaller amounts of impurities. However, crude alkyl phenol mixtures are nor- .mally exceedingly complex systems, so that with crude allqrl phenols from different sources, it may be necessary to determine 'experimentally the type of extraction best suited Hto the particular source, as well as the most economical amount to berecovered as raffinate.

While the effectiveness of the alkyl phenols as anti-oxidants and gum inhibitors is most dependent upon the `relative acidity of the fractions, it may also depend to some degree on the boiling range. 'I'hus we havel found that the weakly acidic alkyl phenol fractions separated from an alkyl mixture having a boiling range betweenfabout 210 to 270 C. are usually more effective than the fractions extracted from other distillation cuts. It is further often advantageous in separating the weakly acid alkyl phenols according to their acidity first to divide the crude alkyl phenolmixture into various distillate fractions of narrow boiling ranges, preferably covering not more than about C., and then separating the'several weakly acidic fractions. A The latter may be used separately or combined for inhibiting purposes. By this method it is often possible tosecure the greatest yield of alkyl phenols having the highest inhibiting value possiblefifrom a given crude mixture.

The following is an example of a fractional extraction of crude alkyl phenols, showing the inhibiting values of the weakly acidic fractions to'be much higher than those of the bulk alkyl phenols or their morestrongly acidic fractions:A

lBulk or crude alkyl phenols. obtained by extraction with 40 B. caustic soda from a Mid- Continent cracked gasoline having a boiling range of 40 to 200 C., were separated into 15 cuts of successively decreasing acidities by frac- -tional extraction as follows: Y

A solution of 1200 ml. of the bulk alkyl phenols Jin 4000 ml. of peroxide free diisobutylene was extracted in six successive extractions with six 250 ml. portions of 5 B. sodium hydroxide solution, and the remaining portion was thentreated with an amount of an aqueous solution of 50 B.

- sodium hydroxide containing an excess of hydroxide., whereby a phenolate solution was obtained. In the rst and second extractions only two layers were formed, but in the third through the sixth extractions three layers were obtained. 'I'he six lower'extract layers containing themost strongly acidic alkyl phenols-were separated and acidifled. and the liberated phenols were designated as cuts 1 through 6. 'I'he four middle layers consisting of mixtures of water, free alkyl phenols and diisobutylene were treated with 10 B. sodium hydroxide to remove diisobutylene, the resulting aqueous layers were acidied and the alkyl phenols so obtained were designated as cuts 'I through 10.

- The 50 B. phenol'ate solution was then acidifled, the alkylphenols so liberated were redissolved in 1200 c. c. of diisobutylene and the resulting solution wasv extracted with ve successive 100 c. c. portions of .10 B. sodium hydroxide. 'The alkylV phenols liberated from the ve caustic portions constituting the most weakly acidic v fractions were designated Aas cuts 11 through 15. Only a trace of 'phenols remained in the diisobutylene.

The effectiveness as gum inhibitors of the various cuts is shown in the following table:

Addition g3g ma! gms. dilsobutylene Addition 15 Bulk phenols The above example is further illustrated in the drawing in which the anti-oxidant effects of the various cuts are shown graphically. As a reference point, the anti-oxidant eiect of 1,2,4,xylenol, a well-known antioxidant, under the same .conditions is shown.

We claim as our invention: l

1. In the process of inhibiting the oxidation of a hydrocarbon susceptible to oxidation and capable. of being inhibited with alkyl phenols the steps of extracting a mineral oil containing alkyl phenols and thiophenols naturally occurring therein, with strong aqueous caustic alkali thereby producing an alkyl phenol mixture containing thiophenols, reextracting said mixture with a weaker aqueous caustic alkali solution to form two layers, an extract layer containing the aqueous caustic alkali solution of thiophenolsl and strongly acidic alkyl phenols, and a rafdnate layer substantially free from thiophenols and comprising the more weakly acidic alkyl phenols, and adding a small amount of said raffinate to the hydrocarbon.

2. In the process of inhibiting the oxidation' of hydrocarbons susceptible to oxidation and capable of being inhibited with alkyl phenols, the steps of extracting with relatively weak aqueous caustic alkali a mixture of alkyl phenols naturally occurring in mineral oils and having been separated therefrom by extraction with strong aqueous caustic alkali, to produce an extract containing relatively strongly acidic alkyl phenols '-and a railinate containing relatively weakly acidic alkyl phenols, and adding a small amount of said ramnate to said hydrocarbons.

3. In the process of inhibiting the oxidation of hydrocarbons susceptible to oxidation and capable of being inhibited with alkyl phenols. the steps of extracting with relatively weak aqueous caustic alkali, a mixture of allwl phenols having a boiling range of 210 C. to 270 C., naturally occurring in mineral oils and having been separated therefrom by extraction with aqueous caustic alkali of about 30% to 50% concentration to produce an extract containing relatively strongly acidic alkyl phenols and a raillnate containing relatively weakly acidic alkyl phenols and adding a small amount of said raillnate to drocarbon oil and an added amount of an alkyl phenol fraction, said fraction comprising'a relatively weakly acidic portion, of a crude mixture of alkyl phenols naturally occurring in mineral oils and having been separated therefrom by extraction with strong caustic alkali, said fraction n having been obtained by fractionally extracting said mixture with weaker aqueous caustic alkali.

5. A composition'of matter comprising a. hy-

drocarbon oil and an added amount of an alkyl phenol fraction separated from a crude alkyl phenol mixture naturally occurring in mineral oils andy having been separated therefrom by extraction with strong caustic alkali, said mixture having a boiling range of from 210 C. to 270 C., said fraction having. been obtained by extracting said mixture with a yweaker aqueous solution of a caustic alkali and being more weakly acidic than the average of said mixture.

WILBUR E. ROBBINS. RICHARD R. ZUNDEL. 

